KnowledgeBase Archive

An Archive of Early Microsoft KnowledgeBase Articles

View on GitHub

Q180903: PRB: LCK Functions Do Not Work in a Private Data Session

Article: Q180903
Product(s): Microsoft FoxPro
Version(s): WINDOWS:5.0,5.0a,6.0
Operating System(s): 
Keyword(s): kbvfp kbvfp500 kbvfp600
Last Modified: 11-DEC-1999

-------------------------------------------------------------------------------
The information in this article applies to:

- Microsoft Visual FoxPro for Windows, versions 5.0, 5.0a, 6.0 
-------------------------------------------------------------------------------

SYMPTOMS
========

An ActiveX control (.ocx) has been written in Visual C++ that also makes use of
the Visual FoxPro Library Construction Kit (LCK) functions. The control may work
properly on forms that use the default DataSession but the control fails when
the form uses a private DataSession.

CAUSE
=====

Library Construction Kit function calls do not occur in the DataSession context
of the form that made the call to the .ocx. There is only one global context in
which the Library Construction Kit function can call into Visual FoxPro, no
matter where the call originated.

RESOLUTION
==========

If a private DataSession is necessary, write the ActiveX control completely in
Visual C++ or Visual Basic and expose properties and methods that can be
accessed by Visual FoxPro.

If it is absolutely necessary to use some of the Visual FoxPro LCK functions in
an .ocx that will access tables in a private DataSession, it may be possible to
get the .ocx to work by making the private DataSession the active DataSession by
using the SET DATASESSION TO <nDataSessionNumber> command. However, this
approach is not recommended. Writing the functionality into the control with
another language is a better solution.

STATUS
======

This behavior is by design.


MORE INFORMATION
================

FoxPro and Visual FoxPro have included the Library Construction Kit for many
versions. The Library Construction Kit functions allow developers to write
libraries in C that can be loaded by FoxPro or Visual FoxPro to extend its
functionality by accessing the FoxPro API. Starting with Visual FoxPro version
5.0, the Developer's Guide has included information to help developers get a
start on creating ActiveX controls to access the Visual FoxPro API. ActiveX
controls can make use of the LCK functions if used within the global context of
Visual FoxPro.

Library Construction Kit functions that access tables that may be open in private
DataSessions, such as _DBRead and the other _DBxxxx functions, _Load, _FindMemo
and _FindVar, are some of the functions to avoid in ActiveX controls that need
to work in private DataSessions. However, depending on what the ActiveX control
does and how it does it, other LCK functions may also fail in private
DataSessions. A good test is to try the control in the default DataSession. If
it works there and not a private DataSession, this article probably applies.

REFERENCES
==========

Microsoft Visual FoxPro "Developer's Guide," version 5.0, pages 645-647.

Examples.dbf located in the \API\Samples folder of Visual FoxPro.

Microsoft Visual FoxPro Help: Library Construction Kit.

Additional query words:

======================================================================
Keywords          : kbvfp kbvfp500 kbvfp600 
Technology        : kbVFPsearch kbAudDeveloper kbVFP500 kbVFP600 kbVFP500a
Version           : WINDOWS:5.0,5.0a,6.0
Issue type        : kbprb

=============================================================================

THE INFORMATION PROVIDED IN THE MICROSOFT KNOWLEDGE BASE IS PROVIDED "AS IS" WITHOUT WARRANTY OF ANY KIND. MICROSOFT DISCLAIMS ALL WARRANTIES, EITHER EXPRESS OR IMPLIED, INCLUDING THE WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. IN NO EVENT SHALL MICROSOFT CORPORATION OR ITS SUPPLIERS BE LIABLE FOR ANY DAMAGES WHATSOEVER INCLUDING DIRECT, INDIRECT, INCIDENTAL, CONSEQUENTIAL, LOSS OF BUSINESS PROFITS OR SPECIAL DAMAGES, EVEN IF MICROSOFT CORPORATION OR ITS SUPPLIERS HAVE BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES. SOME STATES DO NOT ALLOW THE EXCLUSION OR LIMITATION OF LIABILITY FOR CONSEQUENTIAL OR INCIDENTAL DAMAGES SO THE FOREGOING LIMITATION MAY NOT APPLY.